Redmond Way Storm Trunk

Redmond Way Storm Trunk is mostly complete, providing a high capacity pipe through downtown. The new outfall connection to the Sammamish River will be constructed along with the Redmond Way Water Quality Facility. This project has been partially funded by grants from the Washington State Department of Ecology.

The proposed media filter water quality facility will retrofit the entire watershed, providing protection to the Sammamish River from urban runoff.

What is a Media Filter?

A media filter is a type of filter that uses a bed of sand, compost, crushed granite or other material to filter water for drinking, swimming pools, aquaculture, irrigation, stormwater management and other applications. Media filters can be effective at removing pollutants in stormwater such as suspended solids, dissolved metals, oil & grease, and phosphorus. Sand was the first widely used filter for stormwater.

These sand filters were later amended with compost, zeolite, perlite, granular activated carbon, and other media to improve removal of various pollutants. Filters have been modified using various mechanical configurations to improve flow rates and reduce maintenance requirements. Porous concrete is a media that has recently been explored for use in stormwater treatment.

What type of media filter is proposed for this project?

The City had been hoping to use Royal Enterprises’ EcoStorm Plus porous concrete filter for this project. That technology had high promise, and was constructed as a pilot project across the street in 2007. Although that product ultimately has been approved by Ecology, the high maintenance demand is not acceptable to the City. During the summer of 2013, prior to making a final selection of the preferred treatment alternative, the City reopened the alternatives analysis.

The City wanted to reconfirm that the regional approach proposed by this project is the right one, and that the use of EcoStorm Plus was the right treatment technology to use. Through that new analysis, five scenarios were evaluated: 1) Basin Planning 2) Fully Distributed 3) EcoStorm 4) Passive Filter, and 5) Active Treatment. Life cycle cost analysis, site constraints, and other factors led to selection of the passive media filter for this project. That analysis is documented in the project design report.

The regional approach was confirmed, and the selected media filter is Contech’s StormFilter. The City has experience with the StormFilter product, with several installations in public and private applications in Redmond. The product has been in used in the United States for two decades. The filter is a cartridge based system that will use a media composed of zeolite, perlite, and granular activated carbon.

Design Information

Redmond Way Water Quality Facility

This underground system is in final design and will be a large Stormfilter vault facility with a pump station. This project is being partially funded by the Washington State Department of Ecology’s FY2011 Stormwater Retrofit Grant Program.